1. Field of the Invention
The present invention relates to inkjet ink and an inkjet recording method.
2. Description of the Related Art
So-called inkjet systems in which a liquid or melt solid ink is discharged through an ink discharge port such as a nozzle, a slit and a porous film are used in many printers due to their characteristics such as small size and low cost. Among these inkjet systems, a piezo-inkjet system for discharging ink utilizing deformation of a piezoelectric element and a thermal inkjet system utilizing the boiling of ink caused by the thermal energy are frequently utilized from the viewpoint of the high resolution and the high speed printability. In addition, an inkjet printer can print not only on a so-called paper such as a plain paper, a paper exclusively for inkjet but also on a film such as an OHP sheet, a cloth and the like.
For the purpose of the long-term storage stability, there is proposed use of a solvent represented by the following formula (II) as an organic solvent (for example, see Japanese Patent Application Laid-Open (JP-A) No. 05-17714). In order to secure the long-term storage stability, it is necessary to prevent water from evaporating. In the prior art, from such a viewpoint, a solvent represented by the general formula (II) has been used as a humectant. However, in a case of a kind of ink in which a pigment and a solvent represented by the general formula (II) are combined, reduction in the storage stability associated with aggregation of a pigment occurs in some cases.HO—(CHR—CH2—O—)n—H  General formula (II)[In the general formula (II), n represents an integer, and R represents hydrogen or an alkyl group.]
In addition, for the purpose of improving the long-term storage stability, the drying property in a plain paper, the printing quality, the water resistance and the abrasion resistance, there is provided a kind of ink for inkjet recording containing water, a pigment which is self-dispersible in water and a water-soluble organic solvent, and containing a water-soluble organic compound having the S.P. value of 12 or smaller and the surface tension at 25° C. less than 40 mN/m in an amount of 3.0% by mass to 15.0% by mass relative to a total mass of ink (JP-A No. 11-228898). Example of the same reference shows a kind of ink in which triethylene glycol is added as another additive, but it was found that when such the ink is stored for a longer period of time, the storage stability is insufficient.
In addition, there is provided an image forming method of using an ink composition containing a coloring material having at least one carboxyl group, and a multivalent metal salt solution, adding the multivalent metal salt solution to a recording material and, thereafter, printing using the ink composition (for example, see JP-A No. 05-202328). An object of this method is to improve the water resistance and color bleeding, but when a pigment is used as a coloring material, the long-term ejection stability is reduced in some cases.
As described above, according to the conventional methods, the long-term ejection stability, the long-term storage stability, the optical concentration, the bleeding and the water resistance can not be satisfied at the same time.